E47 activates the Ig-heavy chain and TdT loci in non-B cells

The E2A proteins, E12 and E47, are basic helix-loop-helix (bHLH) proteins essential for the B-cell lineage. Initially identified as immunoglobulin enhancer-binding proteins, they have also been shown to activate immunoglobulin enhancer-based reporters in transient transfection assays, Here, we examine the relationship between E2A DNA binding activity and activation of the endogenous, chromosomal immunoglobulin heavy chain (IgH) locus, Using sterile I mu transcription as an indicator of IgH enhancer activity, we see a direct correlation between E2A DNA binding activity and I mu transcription in stable BxT hybrids. We also observe a 1000-fold stimulation of endogenous ICL transcription in fibroblasts that express high levels of E47 and less stimulation in cells that express E12, By contrast, none of the other IgH enhancer-binding proteins tested (E2-2, Pu.1, Oct-2, OCA-B, TFE3 and USF) were able to activate I mu transcription, E47 overexpression also resulted in transcriptional activation of the endogenous gene encoding TdT, indicating that it, too, is a target of E2A proteins early in the B-cell lineage, Our results indicate that E2A proteins have the distinctive property of activating silent, chromatin-embedded B-cell-specific genes, underscoring their crucial role in B-cell development.